Analysis of Offshore Structures Subjected to Various Types of Sea Wave

2004 ◽  
Author(s):  
K. Kuntiyawichai ◽  
S. Chucheepsakul ◽  
M. M. K. Lee
Keyword(s):  
Finite Element ◽  
Wavelet Analysis ◽  
Dynamic Behaviour ◽  
Time History ◽  
Offshore Structures ◽  
Offshore Platforms ◽  
Wave Loading ◽  
Offshore Structure ◽  
Finite Element Software ◽  
Jacket Structures

The principal aim of this paper is to study the dynamic behaviour of offshore platforms subjected to wave loading. A general review of offshore structure, wave loading and their effects on offshore structures are presented. A brief review on the basics of Wavelet analysis is also mentioned in this study. The techniques for modeling wave loading in finite element analyses are described and discussed in detail. A series of 3D analyses were carried out using the ABAQUS finite element software to study the effects on the dynamic response of the change in support conditions at the seabed. The effects of wave height, wave period and wave velocity on platform behaviour were studied. The results from time history analysis are characterized using Wavelet Analysis in order to obtain the response pattern due to wave loading. These analyses allow the frequency response of the jacket structures to be described in the time domain. These results give a clear view on the response of jacket structure. The important parameters on offshore modeling have also been identified and discussed in this paper. The results presented in this study can be used as a guidance for engineer in order to understand the dynamic behaviour of jacket structures subjected to wave loading.

Finite Element Analysis for Structural Performance of Offshore Platforms under Environmental Loads

2013 ◽  
Vol 569-570 ◽  
pp. 159-166 ◽  
Author(s):  
Shehata E. Abdel Raheem ◽  
Elsayed M.A. Abdel Aal
Keyword(s):  
Finite Element ◽  
Return Period ◽  
Wave Force ◽  
Offshore Structures ◽  
Offshore Platform ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Current Increase ◽  
Environmental Loads ◽  
Highly Nonlinear

Offshore structures for oil and gas exploitation are subjected to various ocean environmental phenomena which can cause highly nonlinear action effects. Offshore structures should be designed for severe environmental loads and strict requirements should set for the optimum performance. The structural design requirements of an offshore platform subjected to wave induced forces and moments in the jacket can play a major role in the design of the offshore structures. For an economic and reliable design; good estimation of wave loadings are essential. The structure is discretized using the finite element method, wave force is determined according to linearized Morison equation. Hydrodynamic loading on horizontal and vertical tubular members and the dynamic response of fixed offshore structure together with the distribution of displacement, axial force and bending moment along the leg are investigated for regular and extreme conditions, where the structure should keep production capability in conditions of the one year return period wave and must be able to survive the 100 year return period storm conditions. The results show that the nonlinear response analysis is quite crucial for safe design and operation of offshore platform. Fixed Jacket type offshore platforms under extreme wave loading conditions may exhibit significant nonlinear behavior. The effect of current with different angles when hitting the offshore structure with the wave and wind forces, is very important for calculate the stress, the response displacement and deformation shapes. As the current increase or decrease the effect of wave force according to the hitting angle of current.

Integrity Management System for Fixed Offshore Structures Inspection Strategy

2004 ◽  
Author(s):  
Mohamed A. El-Reedy
Keyword(s):  
Management System ◽  
Offshore Structures ◽  
Assessment Method ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Structure Comparison ◽  
Actual Structure ◽  
Existing Structures ◽  
Integrity Management

The GUPCO offshore structure management system was developed as a part of an integrated infrastructure management system. This paper presents a case study of providing an integrity management system for inspection, evaluation and repair of the fixed offshore platforms in Gulf of Suez. The management system procedure is presented focusing on the first step for defining the highly risky weight to the lower risky weight structure based on API criteria for assessment of the existing structures. The risk analysis methodology for developing design and assessment criteria for fixed offshore structure based on consequence of failure is illustrated. In our case study the assessment method is applied for a number of fixed offshore structures. The above methodology is performed after theoretical assessment and then verifying by using ROV subsea inspection for the fixed offshore structure. Comparison between the actual structure performance and the predicting risk assessment for the structure from the model will be studied. The overall management system will be illustrated in scope of predictive maintenance philosophy and reliability for all offshore structures.

Optimal Vibration Control Strategy for Offshore Platforms Accounting for AMD Constraints

2004 ◽  
Author(s):  
Chunyan Ji ◽  
Qingmin Meng
Keyword(s):  
Control Algorithm ◽  
Feedback Gain ◽  
Offshore Platforms ◽  
Control Force ◽  
Wave Loading ◽  
Offshore Structure ◽  
H2 Control ◽  
Input Control ◽  
The Mathematical Model ◽  
H2 Optimization

In order to control the excessive vibration of offshore platforms under wave excitations, an H2 control algorithm was presented in this paper. In the present study, noise terms for generating filtered wave loading and accounting for model uncertainty are separated. In addition, in H2 optimization problem, AMD’s capacities are considered by setting the limits of AMD stroke and maximum input control force. And the formulations of such algorithm are described. In order to investigate the feasibility and effectiveness of the proposed method, a numerical example applied to an offshore platform is presented in this paper. The numerical results demonstrate that the proposed algorithm is effective in reducing the vibration of offshore structure when there are some uncertainties in building the mathematical model of the structure. In addition, AMD designed by the proposed method can keep its operation by choosing appropriate feedback gain among several gain candidates based on the AMD limits.

scholarly journals The Key Construction Technology Research on the Intercontinental Shanghai Wonderland

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Peng Jiang ◽  
Shaole Yu ◽  
Wei Luan ◽  
Xinxi Chen ◽  
Yang Qin ◽  
...  
Keyword(s):  
Finite Element ◽  
Dynamic Response ◽  
Safety Margin ◽  
Time History ◽  
Construction Technology ◽  
Construction Process ◽  
Component Size ◽  
Finite Element Software ◽  
Deep Pit ◽  
The Stability

The Intercontinental Shanghai Wonderland is the first natural ecological hotel built in an abandoned mine in the world, which faces many difficulties in the construction process. To solve the difficult problems in the construction process, the study was carried out from the stability analysis of the deep pit cliff, the mechanical performance of the structure, and the construction technology. The Intercontinental Shanghai Wonderland is built around the abandoned deep pit cliffs, and the stability of the deep pit cliffs directly affects the safety of the building. The dynamic response characteristics and the instability characteristics of the mine slope under the dynamic response were analyzed by a three-dimensional dynamic finite element method. The calculation results showed that with effective anchoring support measures, the stability coefficient of slope under static load and small earthquakes was large, which had a certain safety margin. Under the action of large earthquakes, the slope could still meet the stability requirements. The structure of the Intercontinental Shanghai Wonderland is a unique two-point support structure system. It shows the deformation and stress characteristics of one fixed end and one simply supported end under horizontal load. The elastic-plastic time history response of structures under actions of rare earthquakes was analyzed through the finite element analysis software. The analysis results show that the current structural system along with the design of component size and strength can meet the seismic performance of the structure under actions of rare earthquakes. The Intercontinental Shanghai Wonderland was built in a stone pit 88 m below the surface. Therefore, the transportation of materials was a difficulty in the construction process. A set of ultradeep concrete downward conveying equipment was invented to solve the difficulty. The construction process of the whole structure was simulated by finite element software, which provided a safety guarantee for the construction of the whole structure.

Effect of Seabed Slope on Offshore Pile Lateral Behaviour Under Wave Force

2010 ◽  
Author(s):  
Sathyanarayanan Dhandapani ◽  
Muthukkumaran Kasinathan
Keyword(s):  
Finite Element ◽  
Vertical Direction ◽  
Pile Group ◽  
Element Model ◽  
Wave Force ◽  
Wave Forces ◽  
Extreme Conditions ◽  
Offshore Platforms ◽  
Wave Loads ◽  
Offshore Structure

Fixed offshore platforms supported by pile foundations are required to resist dynamic lateral loading due to wave forces. The response of a jacket offshore tower is affected by the flexibility and nonlinear behavior of the supporting piles. In this study, a typical fixed offshore platform is chosen, and dynamic wave analysis is performed on it. Analysis has been performed for normal environmental conditions and extreme conditions. For the foundation, the deflections and reactions at regular intervals along the vertical direction from the seabed have been found out from the dynamic analysis, and the results have been compared for normal and extreme conditions. The aim of this study is to investigate the effects of the combined lateral and vertical loads on pile group foundation of a fixed offshore structure and the effects of seabed slope on the pile responses. To provide a more accurate and effective design for offshore pile foundation systems under axial structural loads and lateral wave loads, a finite element model which is modelled in FLAC3D is employed herein to determine the soil structure interaction under similar loading conditions. Three dimensional modelling and the analyses are done using FLAC3D — a finite element package.

Seismic Response Analysis of Twin-Tower Building with Enlarged Base

2014 ◽  
Vol 912-914 ◽  
pp. 1534-1537
Author(s):  
Shao Bo Zhang ◽  
Ke Lun Wei ◽  
Bi Jian Xiao
Keyword(s):  
Finite Element ◽  
Dynamic Response ◽  
Boundary Conditions ◽  
Seismic Response ◽  
Time History ◽  
Response Analysis ◽  
Rigid Boundary ◽  
Finite Element Software ◽  
Elastic Boundary ◽  
Elastic Boundary Conditions

This paper adopts large finite element software ANSYS to establish finite element model of twin-tower building with enlarged base, uses dynamic time history analysis method for seismic response calculation, compare and analyze the calculation results of twin-tower building with enlarged base under elastic boundary conditions and rigid boundary conditions. The results showe that dynamic response for model under elastic boundary conditions is larger than dynamic response for model under rigid boundary conditions, and elastic boundary conditions is more close to the actual situation.

Ice rubble attenuation of ice loads on arctic offshore structures

1991 ◽  
Vol 28 (6) ◽  
pp. 881-895 ◽  
Author(s):  
T. T. Wong ◽  
N. R. Morgenstern ◽  
D. C. Segoz
Keyword(s):  
Finite Element ◽  
Field Measurements ◽  
Offshore Structures ◽  
Force Transmission ◽  
Offshore Structure ◽  
Element Analysis ◽  
Ice Load ◽  
Broken Ice ◽  
Transmission Capability ◽  
Ice Force

A state of the art survey of ice rubble mechanics is first presented. This survey covers ice rubble morphology, laboratory testing of ice rubble, the study of the load transmission capability of existing rubble fields, and field measurements in ice rubble surrounding offshore structures. Then, the implementation of a new plasticity model for normally consolidated broken ice into an existing finite element stress analysis code is described. The resulting program is validated using triaxial test data. Using this model, a two-dimensional parametric study on ice force transmission through a grounded ice rubble field is performed. The study shows that, in addition to the mechanical properties of ice rubble, the island or berm geometry may significantly affect the ice load. Key words: constitutive model, finite element analysis, ice load, ice rubble, offshore structure, plasticity.

Simplified Method to Assess Dynamic Response of Jacket Type Offshore Platforms Subjected to Wave Loading

2004 ◽  
Author(s):  
B. Asgarian ◽  
A. Mohebbinejad ◽  
R. H. Soltani
Keyword(s):  
Dynamic Response ◽  
Dynamic Characteristics ◽  
Offshore Structures ◽  
Center Of Gravity ◽  
Simplified Model ◽  
Mode Shapes ◽  
Stokes Wave ◽  
Wave Crest ◽  
Offshore Platforms ◽  
Wave Loading

Dynamic response of offshore platforms subjected to wave and current is of fundamental importance in analysis. The first step in dynamic analysis is computing dynamic characteristics of the structure. Because of pile-soil-structure and fluid-structure interactive effects in the dynamic behavior, the model is very complex. In this paper a simplified model for dynamic response of jacket-type offshore structures subjected to wave loading is used. Since wave loads on offshore platforms vary with time, they produce dynamic effects on structures. In the model used in this paper, all of the structural elements are modeled as vertical equivalent cylinders that are in the direction of the wave crest. In the simplified model, the degrees of freedom are considered at the seabed, jacket horizontal elevations and topside center of gravity. The stiffness properties of the model are computed considering the stiffnesses of the vertical bracings, legs and piles. The structural mass is considered as lumped nodal masses at horizontal elevations and topside center of gravity. The hydrodynamic added mass in addition to the structural masses was modeled at jacket horizontal elevations. In the simplified model, for computing wave loading, the projected areas of all members in the direction of the wave crest are considered. For the wave loading calculation, Morison equation is considered. The fluid velocities are calculated for the submerged portions of the structures using a computer program developed for this purpose. In this program both Airy and Stokes wave theories can be used. This model can be used to assess dynamic properties and responses of jacket type offshore structures. The model is used to assess the response of three jacket-type offshore platforms in Persian Gulf subjected to loadings due to several waves. The results in terms of dynamic characteristics and responses were compared with the more accurate analysis results using SACS software. The results are in a good agreement with the SACS analysis outputs, i.e. structural periods, mode shapes and dynamic response.

Developing the Structural Integrity Management System for Ageing Fixed Offshore Oil Platforms in Indonesia

2017 ◽  
Vol 862 ◽  
pp. 265-270
Author(s):  
Raditya Danu Riyanto ◽  
Murdjito
Keyword(s):  
Management System ◽  
Structural Integrity ◽  
Offshore Structures ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
Element Analysis ◽  
East Kalimantan ◽  
Ranking Criteria ◽  
Life Years ◽  
Integrity Management

Offshore structure, particularly fixed offshore structures, should be kept in the performance for the fit-for-purpose condition during their operating lifetime. For fixed offshore structures that exceed their designated life years, the proper Structural Integrity Management System (SIMS) should be developed and applied. Despite the fixed offshore platforms have their service life, there are still platforms that continue to operate exceeding their service lifetime. These ageing platforms should be taken care thoroughly to avoid the consequences that could take casualties. This paper will propose the proper initiation of SIMS development for ageing fixed offshore platforms in Indonesia, by taking an example at Bekapai Field Platforms in East Kalimantan. Using HAZID technique and several ranking criteria, the platforms are assessed and ranked. Platforms that categorized in critical condition are grouped based on similarities in geometry and function. The highest rank is analyzed in computer Finite Element Analysis (FEA) Software with modification based on latest inspection result. This method is proven to be a proper method to be used as a maintenance program for ageing fixed offshore platforms in Indonesia.

A Rational Approach to Automated Pre- and Post-Processing of Offshore Structure Global Strength Finite Element Analysis

2011 ◽  
Author(s):  
Zhiyong Yang ◽  
Otto DaSilva
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Rational Approach ◽  
Strength Analysis ◽  
Complex Nature ◽  
Post Processing ◽  
Offshore Structure ◽  
Element Analysis ◽  
Finite Element Software ◽  
Global Strength

Offshore structure global strength analysis based on finite element plate model is a requirement for today’s classification societies and designers. Wave, wind, current loads have to be applied to the global strength model as a pre processing step to allow the analysis to take place. After the analysis, code checking must be performed to verify if the structure meets class or other requirements. Due to its complex nature, a large amount of engineering hours have to be spent for the pre and post processing. This is not only lengthy if performed manually or semi-automatically, but also mistake prone. General guidelines from classification societies exist, but general purpose commercial software is scarce and often still requires significant amount of engineering time to perform these tasks. This paper shows a rational approach to automate the pre and post processing of offshore structure global strength finite element analysis. Utilizing the FEMAP Application Program Interface (API), a complete automatic pre and post processing is implemented in one integrated program, Exmar Design Suite (EDS). The program will load the model from WAMIT generated wave pressure, apply internal pressure induced from motions to internal tanks, and also apply other environmental loads. After the finite element analysis, the program can execute strength code checking including yielding and buckling for the model. Both beam and stiffened plate panels can be identified using an automatic search algorithm, which is not a function available for general finite element software. The panels and beams are then checked against various common codes such as API/AISC/ABS/DNV. In addition, fatigue analysis can also be performed in either spectral or simplified approach. The benefits of automation are timesaving, accuracy and reliability. It also makes the check of whole model possible. Instead of relying more on “screening” or experience based structure check, engineers will have more confidence in the results by going through the whole model.

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